Organic deposits derived from crude oil have long been a source of trouble and operating expense to petroleum producers. These organic deposits may be almost totally paraffinic in nature or they may be highly asphaltic, depending on the particular crude oil produced. The deposits accumulate in tubular goods, production and storage equipment, and pipelines as well as on the faces of producing formations in oil and water wells. As the organic deposits build up in production equipment, tubular goods, and related apparatus, production is gradually decreased until remedial work is required to remove the deposits. Heretofore, removal of such organic deposits has been accomplished by mechanical scraping of the surfaces of equipment utilizing knives, scrapers, and similar devices, and also by dissolving the deposits in solvents such as hot crude oil and kerosene.
While solvents such as hot crude oil and kerosene are relatively effective for dissolving organic deposits which are paraffinic in nature, they are relatively ineffective for dissolving asphaltenic compounds. In general, organic deposits of high asphaltenic compound content are hard and brittle while deposits formed primarily of paraffinic compounds are soft and pliable. Thus, deposits containing asphaltenic compounds have heretofore been particularly troublesome to oil producers in that they are difficult to remove by mechanical methods and conventional solvents are relatively ineffective in their removal. Stripping asphaltenes from mineral surfaces is discussed in an article by Jeffries-Harris et al. entitled "Solvent Stimulation in Low Gravity Oil Reservoirs" which appears in the February 1969 issue of the Journal of Petroleum Technology at page 171. The author discloses the use of a standard well stimulation solvent, diesel oil, by itself and in combination with certain additives to dissolve asphaltenes. Some of the materials utilized by Jeffries-Harris include diesel oil; diesel oil-5% xylene; diesel oil-5% xylene-1%n-butyl amine; diesel oil-1% n-butylamine; diesel oil-5% toluene; and diesel oil-1/4% hexylamine. The combination of diesel oil and 1% n-butylamine appeared to be substantially superior to diesel oil alone with respect to dissolving asphaltenes, but the combinations diesel oil-5% xylene-1% n-butylamine, diesel oil-5% xylene, and diesel oil-5% toluene appeared to provide very little, if any, improvement to the solvent power of diesel oil.
Gary Sutton's U.S. Pat. No. 3,914,132 issued Oct. 21, 1975 expanded upon this method of treatment by demonstrating the synergistic effects of amines and aromatic solvents on dissolving asphaltenic deposits. U.S. Pat. No. 3,914,132 discloses the invention consisting of a mixture of an aromatic solvent (benzene, toluene, xylene) and an amine selected from the group of pyridine, morpholine, and primary, secondary and tertiary amines defined by the general formula: ##STR1## where R, R', and R" represent members selected from the group consisting of hydrogen, alkyl radicals having from 1 to 4 carbon atoms, cycloaklyl radicals having from 1 to 4 carbon atoms, cycloalkyl radicals having from 3 to 6 carbon atoms and mixtures thereof. He demonstrated the increased solubility of asphaltenic deposits in aromatic solvents with the inclusion of a relatively small amount of an amine (5% ethylenediamine).
The references cited in U.S. Pat. No. 3,914,132 are as follows:
United States Patents:
______________________________________ 1,643,675 9/1927 Montgomerie 252/311.5 2,509,197 5/1950 Borus et al 252/153X 2,685,523 8/1954 Cross, Jr., et al. 106/278X 2,750,343 6/1956 Beber 252/153 2,904,458 9/1959 Dykstra 252/153X 3,137,730 6/1964 Fitz-William 260/583P X 3,279,541 10/1966 Knox et al. 252/8.55B X 3,914,132 10/1975 Sutton 134/40 ______________________________________
Other Publications:
Jeffries-Harris et al. "Solvent Stimulation in Low Gravity Oil Reservoirs" Journal of Petroleum Technology, February 1969; pp. 167-175.
We have now discovered that a composition comprising
(1) an aromatic solvent, and
(2) a hydrocarbon-substituted-alkarylsulfonic acid such as an alkylbenzene sulfonic acid can be used to effectively remove organic deposits containing asphaltic constituents.
Any effective hydrocarbon-substituted-alkarylsulfonic acid can be employed. In practice, an alkylbenzenesulfonic acid is employed where the alkyl group has at least about 5 carbon atoms, for example, from about 5 to 20 carbon atoms, such as from about 8 to 18 carbons, but preferably from about 10 to 14 carbon atoms. A polyalkyl-benzenesulfonic acid can be employed provided the total carbons in the alkyl groups have the above carbon value.
Any effective concentration of alkylbenzenesulfonic acid can be employed. The effective amount will depend on many variables, such as the particular sulfonic acid, the particular solvent, the particular system, etc. In practice, we employ about 1 to 80% by weight of the sulfonic acid in the solvent, e.g., from about 2 to 50, or from about 5 to 40, for example, from about 5 to 30, but preferably from about 10 to 25.
The preferred solvent comprises a liquid aromatic hydrocarbon, for example benzene, toluene, and xylene; or mixtures thereof.
In certain instances where the oil produced is rich in aromatic hydrocarbons, the alkarylsulfonic acid (100%) may be added to or dissolved in the produced oil. Mixtures of alkyl benzenesulfonic acids have also been employed.